The efficiency of all chromatographic methods (i.e. column or planar and gas or liquid chromatographies) is largely dependent on the properties of the chromatographic media. Therefore, extensive research efforts have been devoted to the invention of a plethora of chromatographic packings tailored for a variety of specific separation needs. Silica based packings are particularly suitable for chromatographic applications since they are thermally stable, chemically inert, can be manufactured in various geometrical configurations and their pore size and bulk density can be predetermined. Moreover, the polarity of silica based matrices can be modified by covalent bonding of organic compounds onto the polar glass matrix (R. E. Majors, J. of Chromatographic Science, 15, 334 (1977)) or by impregnation of the silica gel glass with organic compounds (E. Stahl, Thin Layer Chromatography, 2nd ed., Springer-Verlag, Berlin (1969) p. 48).
The recent new innovation of doped sol-gel glasses (described in the U.S. Pat. application Ser. No. 07/637,873) provides a new class of ceramic packings for chromatography that incorporates characteristics of silica glasses as well as other advantages:
1. The characteristics of the sol-gel glasses, including glass configuration, pore size, density and glass polarity can be tailored to any required need. These can be achieved, for example, by changes of the ratio between the alkoxysilane/water/alcohol in the polymerization solution, or by incorporation of trialkoxysilane compounds in the polymerization solution (Brinker, C. J., Scherer, G. W., Sol-Gel Science, Academic Press, San Diego (1990)).
2. The exact chemical characteristics of the solid support including their interaction with the target chromatographic compounds can be controlled by suitable chemical dopants. A wide range of compounds including ion exchange compounds (such as those containing carboxylic, sulfonic, aminic and ammonium groups) have been successful entrapped in solid sol-gel glasses in a relatively simple procedure.
3. The doped sol-gel glasses maintain the transparency of the sol-gel glasses except for the absorbance window of the dopants. This property is particularly important for such chromatographic methods where visualization and quantitation of the separated compounds are manifested when the compounds are still in the chromatographic media (e.g. Thin Layer Chromatography and spot tests which are discussed below).
4. The doped sol-gel glasses are highly porous even when chemical dopants are incorporated into the polymerization step.
5. The chemical modification of the sol-gel glass by the doping process is more stable than impregnated layers and more simply performed than covalent bonding of organic coatings.
In the following we shall present typical chromatographic and spot test applications demonstrating the possibility to use doped sol-gel glasses for planar or column chromatographic applications in gas or liquid analysis. The chromatographic applications and the ion exchange properties of doped sol-gel glasses were disclosed in the U.S. patent application No. 07/637,873 without experimental demonstration. Analytical spot testing and length of stain detectors were disclosed but were not mentioned specifically in the patent application.